The present invention relates to a TFT (thin film transistor) array inspection apparatus for inspecting a thin film transistor array substrate used for a liquid crystal display, an organic electro-luminescent display and the like.
As a TFT substrate inspection apparatus, there has been known an apparatus for inspecting a defect in which a probe of an oscilloscope contacts a TFT substrate to obtain a signal waveform. In such an apparatus, it is necessary to mechanically move the probe to contact the TFT substrate, thereby taking a long time for the inspection. To solve the problem, there has been known an apparatus for performing a GO/NG inspection in which a defective site on a TFT substrate is optically extracted and a probe contacts the defective site obtained through the GO/NG inspection to thereby inspect the TFT substrate.
However, even in an apparatus for performing the GO/NG inspection, after a defective site is detected, the probe needs to contact the TFT substrate. As described above, in the TFT substrate inspection using the probe, a tip of the probe needs to directly contact a surface of the TFT substrate, thereby causing a risk of damaging the TFT substrate. In addition to the problem of damaging the substrate, it is mechanically difficult to position the probe at a specific pixel on the TFT substrate. Especially when the TFT substrate has a large size, since a stage for supporting the TFT substrate has a limited positioning accuracy, it is difficult to accurately position the probe. Also, since the probe mechanically contacts the TFT substrate, it is difficult to secure reliable contact, thereby making it difficult to distinguish a loose contact of the probe from the defect.
In contrast with the TFT substrate inspection through the probe contact, there has been proposed a non-contact TFT substrate inspection apparatus without using the probe. Such a TFT substrate inspection apparatus inspects the TFT array through irradiating an electron beam on the TFT array and detecting a discharged secondary electron to inspect the TFT array with a voltage contrast phenomenon. In the voltage contrast phenomenon, when an electron beam is irradiated on a sample, a secondary electron is discharged from the sample surface. An energy distribution of the secondary electron is shifted in proportion to a voltage applied to the sample. A voltage of the TFT substrate is measured to detect a change in the secondary electron, and it is determined whether the measured voltage is a predetermined voltage to inspect the TFT substrate. Such a TFT substrate inspection apparatus as described above has been disclosed in, for example, Japanese Patent Publication (Kokai) No. 2000-3142, or Japanese Patent Publication (Kokai) No. 11-265678.
In the conventional TFT substrate inspection apparatus including the inspection apparatus using the probe or the non-contact inspection apparatus using the electron beam, there has been a problem that a long period of time is required in order to carry out a detailed defect inspection at a specific site of the TFT substrate.
In the inspection apparatus using the probe, the probe is moved relative to the TFT substrate and contacts a pixel at the moved position for the defect inspection repeatedly. Therefore, a long inspecting time is required to inspect the whole surface of the TFT substrate.
In the inspection apparatus using the electron beam, the electron beam is irradiated at an extremely small region relative to the TFT substrate. Accordingly, it is necessary to irradiate the electron beam at positions sequentially relative to the TFT substrate to inspect a defect over the entire surface of the TFT substrate as in the inspection using the probe, thereby taking a long inspecting time.
In the conventional inspection apparatuses, even if the TFT substrate contains a few number of sites to be inspected in detail and almost all sites do not require the inspection, it is still necessary to carry out the same defect inspection over the whole surface of the TFT substrate. Thus, it is inevitable to take a long period of time for the inspection. Especially when the TFT substrate has a large size, the problem becomes serious.
In view of the above problems, it is an object of the invention to provide a TFT array inspection apparatus, wherein a time for a detailed defect inspection of a specific site on a TFT substrate is shortened.
Further objects and advantages of the invention will be apparent from the following description of the invention.